The neural basis of adaptive plasticity of the vestibulo-ocular reflex will be studied utilizing behavioral, electrophysiological, neurochemical and morphological techniques in squirrel monkeys. Employing visual-vestibular mismatch stimuli and/or miniaturizing or magnifying lenses placed in a spectacle mount in front of the animals' eyes will adapt the vestibulo-ocular reflex. Both the normal and adapted vestibulo-ocular reflex will be utilized as probes to elucidate the properties of discharge modulation of cerebellar floccular Purkinje cells and brainstem neurons. Previous work suggested that there are multiple brain sites for vestibulo-ocular reflex learning and memory, namely in the cerebellum and brainstem. We will employ paradigms contrasting the acquisition, consolidation and memory of novel VOR gains designed to elucidate which of these sites encode signals that might be causal to the observed behaviors. We will analyze the role of the velocity to position neural integrator in this plasticity. We will determine the role of cerebellar cortical interneurons (e.g. Golgi cells) in shaping the information flow through the cerebellar cortex. We will evaluate potential error signals necessary for learning to proceed in any adaptive system. Our experiments should provide new data to aid in the understanding of the neural basis of learning and memory and will lead to the construction of mathematical models of the actions of cerebellar and brainstem neurons in the acquisition and memory of VOR gain.